In a judgment delivered on 26th July 2017, Comune di Corridonia (joined cases C-196/16 and C-197/16), the CJEU affirmed the approach to regularisation of development which takes place without an environmental impact assessment being undertaken, when such assessment should have preceded the development. The case concerned the construction of two separate plants for the generation of electricity from biogas, which were permitted pursuant to national legislation which was subsequently found to be incompatible with Directive 2011/92.
The CJEU affirmed that regularisation of EIA development must not allow an applicant to circumvent the rules of EU law or to dispense with their application, and that such regularisation should remain the exception: see also Commission v Ireland (case 215/06, paragraph 57), applied domestically in R. (on the application of Padden) v Maidstone BC  EWHC 51 (Admin). It also held that any assessment carried out must take account of not just future impact, but must also consider environmental impact from the time of completion of the development:
“37. The Court has, however, held that EU law does not preclude national rules which, in certain cases, permit the regularisation of operations or measures which are unlawful in the light of EU law (judgments of 3 July 2008, Commission v Ireland, C‑215/06, EU:C:2008:380, paragraph 57; of 15 January 2013, Križan and Others, C‑416/10, EU:C:2013:8, paragraph 87; and of 17 November 2016, Stadt Wiener Neustadt, C‑348/15, EU:C:2016:882, paragraph 36).
38. The Court has made it clear that such a possible regularisation would have to be subject to the condition that it does not offer the persons concerned the opportunity to circumvent the rules of EU law or to dispense with their application, and that it should remain the exception (judgments of 3 July 2008, Commission v Ireland, C‑215/06, EU:C:2008:380, paragraph 57; of 15 January 2013, Križan and Others, C‑416/10, EU:C:2013:8, paragraph 87; and of 17 November 2016, Stadt WienerNeustadt, C‑348/15, EU:C:2016:882, paragraph 36).
39. Consequently, the Court has held that legislation which attaches the same effects to regularisation permission, which can be issued even where no exceptional circumstances are proved, as those attached to prior planning consent fails to have regard for the requirements of Directive 85/337 (see, to that effect, judgments of 3 July 2008, Commission v Ireland, C‑215/06, EU:C:2008:380, paragraph 61, and of 17 November 2016, Stadt Wiener Neustadt, C‑348/15, EU:C:2016:882, paragraph 37).
40. The same is also true of a legislative measure which could allow, without even requiring a later assessment and even where there are no specific exceptional circumstances, a project which ought to have been subject to an environmental impact assessment, by virtue of Article 2(1) of Directive 85/337, to be deemed to have been subject to such an assessment, even if such a measure were applicable only to projects in respect of which consent was no longer subject to a possibility of being directly challenged before the courts because of the expiry of the time limit for bringing proceedings laid down in national legislation (see, to that effect, judgment of 17 November 2016, Stadt Wiener Neustadt, C‑348/15, EU:C:2016:882, paragraphs 38 and 43).
41. Furthermore, an assessment carried out after a plant has been constructed and has entered into operation cannot be confined to its future impact on the environment, but must also take into account its environmental impact from the time of its completion.”
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